Untersuchungen an reinen und mit Wasserstoff bedeckten SiC(100)-Oberflächen mit Hochauflösender Elektronenergieverlustspektroskopie

Balster, T.

Book	PreJuSER-28137

Untersuchungen an reinen und mit Wasserstoff bedeckten SiC(100)-Oberflächen mit Hochauflösender Elektronenergieverlustspektroskopie

Balster, T. (Corresponding author)FZJ*

2000
Forschungszentrum, Zentralbibliothek Jülich

Jülich : Forschungszentrum, Zentralbibliothek, Berichte des Forschungszentrums Jülich 3759, (2000)

Please use a persistent id in citations: http://hdl.handle.net/2128/20605

Report No.: Juel-3759

Abstract: At the cubic silicon carbide (100) surface the fermilevel is pinned mithin the bandgap hy acceptorlike defect states, which are responsible for the creation of a depletion lauer in n-doped semiconductors . Collective surface excitations of Si-terminated (2x 1) and C-terminated c(2 x 2) reconstructions of the SiC(100) surface, i .e. the longitudinal optical phonon of the depletion lauer wa and the coupled oscillations of the plasmon and the longitudinal optical phonon in the bulk w + , the so-called plasmarons, were studied by means of high-resolution electron energy loss spectroscopy. Electron energy loss spectra are cnlculated from classical and seifconsistent electron density profiles in the framework of dielectric tlieorv and compared to the measured spectra. The peak of the elastically reflected electrons is asymmetrically broadened at room perature hy excitation of the plasmaron w - , that could not be resolved as a single loss peak due to the high density-of=states effective mass of cubic silicon carbide and the low electron mobility . The phonon loss structure around 950 cin - , commonly referred as Fuchs- Kliewer-phonon, consists of the LO-phonon of the depletion lauer, the plasmaron ;.v + and the comhination Ioss of w a and the plasmaron The free electron concentration of the bulk could be estimated from the calculation with 2 .2x1018 (111- '3 and 3 .0x 101. i cm -3 for a and a low doped sarnple at room temperature . Other important paraineiters like the density of negatively charged surface states, band bending, electron mobility and plasmon damping factor are determined from the fitted spectra for both reconstructions . The observation of a fermilevel with UPS indicates the existence of a 2-dimensional electron gas (2DEG) at the surface, that generates an additional overdamped plasmon in the outerrnost surface lauer. This 2DEG-plasmon irnproves the fit of the spectra Ihr both reconstructions. Adsorption of atoinic hydrogen an the SiC(100) surface reduces the density of negatively charged surface states, the band bending and the thickness of the depletion lauer of the (2x1) al~d the c(2x2) reconstruction and leads to an increase of the intensity of the plasmaron w + . The free electron concentration of the bulk is lowered by cooling with liquid helium . This decreases the frequency and the intensity of the plasmaron w - . that is responsible for the observed reduction of the FWHI\1 of the quasielastic peak . In the spectra at 35 K additional modes at 625cm-i for the (2x 1) and at 243 and 68 em --1 for the c(4x2) reconstruction are observed, vvhich could be assigned to backfolded accoustical surface phonons . After exposure of the surface to atomic hydrogen those inodes disappear for both reconstructions and the cha,- racteristical vibrations of adsorbed hydrogen are found . At the (2x1) reconstructed SiC(100) surface the SiH stretching vibration at 2142 cm -1 is observed . For the c(2x2) reconstruction the CH stretching vibration of a rnonohydride is found at 2940 cm -1 after lower exposures. From the observation of the symmetric CH2 stretching vibration at 2900 cm - 1 , the antisymmetric stretching vibration at 3000 cm -1 , the syrnrnetric scissor vibration at 1514 cm- 1 and the wagging vibration at 1230 cm -1 it is concluded, that the rnonohydride is transformed into a dihydride after additional hydrogen exposures .

Note: Record converted from VDB: 12.11.2012

Contributing Institute(s):